Rely on upstart's respawn when gerrit stream dies

One of the failure modes is paramiko's SSH client dying.
Trying to work around this while ensuring we don't leak resources
is quite hard; and upstart should be providing the protection
we need against the stream dying already.

Therefore always abort on gerrit stream errors and let upstart's
respawn re-start the process
Merge pull request #26 from BobBall/GerritReconnect

Rely on upstart's respawn when gerrit stream dies